readme: revise conda instructions

This partially reverts 5fb49a5.

Reason: Adding the channels permanently has the advantage of including
pypdfium2 in updates by default. It is also good to tighten channel prio
to be on the safe side.

.github/ISSUE_TEMPLATE/2_conda.yml

@@ -41,8 +41,7 @@ body:
         python -m pip show pypdfium2_raw
         python -m pip show pypdfium2_helpers
         conda list --show-channel-urls "pypdfium2|pdfium-binaries"
-        conda config --get
-        conda info
+        conda config --show-sources
         ```
     validations:
       required: true

README.md

@@ -26,23 +26,37 @@ pypdfium2 includes helpers to simplify common use cases, while the raw PDFium/ct
 
 * <a id="user-content-install-conda" class="anchor" href="#install-conda">From Conda 🔗</a> (official)
   ```bash
-  conda install pypdfium2_helpers -c bblanchon -c pypdfium2-team
+  conda config --add channels bblanchon
+  conda config --add channels pypdfium2-team
+  conda config --set channel_priority strict
+  conda install pypdfium2-team::pypdfium2_helpers
+  ```
+  Adding the channels permanently and tightening priority is optional, but encouraged to include pypdfium2 in `conda update` by default, and to avoid accidentally replacing the install with a different channel.
+  If desired, you may limit the channel config to the current environment by adding `--env`.
+
+  Alternatively, it is possible to allow the channels only once on install, but then you should be cautious when making changes to the environment:
+  ```bash
+  conda install pypdfium2-team::pypdfium2_helpers -c bblanchon -c pypdfium2-team
   ```
-  **Beware:** There have been some third-party attempts to conda package pypdfium2 and pdfium-binaries. Any recipes/packages that might be provided by other distributors, including `anaconda` or `conda-forge` default channels, are [unofficial](#install-unofficial).
 
   To depend on pypdfium2 in a recipe:
   ```yaml
   requirements:
     run:
       - pypdfium2-team::pypdfium2_helpers
   ```
-  You'll want to have downstream callers allow the custom channels on install as shown above, otherwise conda may not be able to satisfy the dependencies.
+  You'll want to have downstream callers handle the custom channels as shown above, otherwise conda will not be able to satisfy requirements.
+  
+  **Beware:** There have been some third-party attempts to conda package pypdfium2 and pdfium-binaries. Any recipes/packages that might be provided by other distributors, including `anaconda` or `conda-forge` default channels, are [unofficial](#install-unofficial).
   
-  To check if the sources are correct:
+  To check the sources are correct:
   ```bash
   conda list --show-channel-urls "pypdfium2|pdfium-binaries"
+  conda config --show-sources
   ```
-  It should show `pypdfium2-team` and `bblanchon` in the channels column.
+  The table should show `pypdfium2-team` and `bblanchon` in the channels column.
+  If added permanently, the config should also include these channels, ideally with top priority.
+  Please confirm this before reporting any issue with a conda install of pypdfium2.
 
 
 * <a id="user-content-install-unofficial" class="anchor" href="#install-unofficial">Unofficial packages 🔗</a>